U.S. patent number 5,061,671 [Application Number 07/516,454] was granted by the patent office on 1991-10-29 for catalyst for the production of alcohols by hydrogenation of carboxylic acids and process for the preparation of the catalyst.
This patent grant is currently assigned to BP Chemicals Limited. Invention is credited to Melanie Kitson, Peter S. Williams.
United States Patent |
5,061,671 |
Kitson , et al. |
October 29, 1991 |
Catalyst for the production of alcohols by hydrogenation of
carboxylic acids and process for the preparation of the
catalyst
Abstract
An improved catalyst comprising a Group VIII noble metal, such
as palladium, and rhenium is supported on a high surface area
graphitized carbon. In an embodiment the Group VIII metal, e.g.,
palladium, has an average crystallite size in the range from 30 to
150 Angstroms. A process for making a catalyst is provided in which
a support is impregnated with a solution of a Group VIII metal
compound, the solvent is removed and the Group VIII metal
impregnated support is impregnated with a solution of a rhenium
compound using a solvent in which the Group VIII metal compound is
insoluble, and thereafter the solvent is removed.
Inventors: |
Kitson; Melanie (Staines,
GB2), Williams; Peter S. (Hull, GB2) |
Assignee: |
BP Chemicals Limited (London,
GB2)
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Family
ID: |
10577615 |
Appl.
No.: |
07/516,454 |
Filed: |
April 30, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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282053 |
Dec 9, 1988 |
4990655 |
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150453 |
Jan 29, 1988 |
4804791 |
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65677 |
Jun 18, 1987 |
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849050 |
Apr 7, 1986 |
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Foreign Application Priority Data
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Apr 13, 1985 [GB] |
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8509530 |
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Current U.S.
Class: |
502/185; 502/339;
502/325 |
Current CPC
Class: |
C07C
29/149 (20130101); C07C 29/149 (20130101); C07C
31/125 (20130101); C07C 29/149 (20130101); C07C
31/08 (20130101); Y10S 502/525 (20130101) |
Current International
Class: |
C07C
29/149 (20060101); C07C 29/00 (20060101); B01J
021/18 (); B01J 023/36 (); B01J 023/64 () |
Field of
Search: |
;502/185,325,339 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0147219 |
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Jul 1985 |
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EP |
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1346638 |
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Feb 1974 |
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GB |
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1491377 |
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Nov 1977 |
|
GB |
|
1551741 |
|
Aug 1979 |
|
GB |
|
Primary Examiner: Shine; W. J.
Attorney, Agent or Firm: Brooks Haidt Haffner &
Delahunty
Parent Case Text
This application is a division of application Ser. No. 07/282,053,
filed Dec. 9, 1988, now U.S. Pat. No. 4,990,655, which, in turn, is
a division of application Ser. No. 07/150,453, filed Jan. 29, 1988,
now U.S. Pat. No. 4,804,791, which, in turn, is a continuation of
application Ser. No. 07/065,677, filed June 18, 1987, now
abandoned, which, in turn, is a continuation of application Ser.
No. 06/849,050, filed Apr. 7, 1986, now abandoned.
Claims
We claim:
1. A process for the production of a catalyst which process
comprises the steps of
(A) impregnating a support with a solution comprising a solvent and
a soluble Group VIII noble metal compound thermally
decomposable/reducible to the Group VIII noble metal and
subsequently removing the solvent therefrom, and
(B) impregnating the Group VIII metal impregnated support with a
solution, in a solvent in which the Group VIII metal is
substantially insoluble, of a soluble rhenium compound thermally
decomposable/reducible to rhenium metal and/or oxide and thereafter
removing the solvent therefrom.
2. A process according to claim 1 wherein the solvent employed in
step (A) is water and the solvent employed in step (B) is
ethanol.
3. A catalyst for comprising palladium and rhenium supported on a
high surface area graphitised carbon wherein the average palladium
crystallite size is in the range from 30 to 99.9 Angstroms.
4. A process as claimed in claim 1 wherein the support is a high
surface area graphitised carbon.
5. A process as claimed in claim 1 wherein the Group VIII noble
metal is palladium.
6. A process as claimed in claim 1 wherein the Group VIII noble
metal is ruthenium.
Description
The present invention relates in general to the hydrogenation of
carboxylic acids. In particular the present invention relates to a
process for the hydrogenation of acetic and propionic acids in the
presence of a catalyst comprising a noble metal of Group VIII of
the Periodic Table of the Elements and rhenium to produce
respectively ethanol and propanol.
The hydrogenation of carboxylic acids to produce the corresponding
alcohol using supported Group VIII noble metal catalysts is known
from, for example, U.S. Pat. No. 4,524,225; U.S. Pat. No.
4,104,478; GB-A-1534232; GB-A-1551741 and EP-A-147219. Of the
aforesaid patents, all except GB-A-1534232 relate to the
hydrogenation of C.sub.4 and higher carboxylic acids and, in common
with GB-A-1534232, to operation in the liquid phase. Moreover,
EP-A-147219 represents an intervening publication in the sense that
it was published after the priority date claimed for the subject
application on an application claiming an earlier priority date
than the subject application.
GB-A-1534232 relates to the production of alcohols by the catalytic
hydrogenation of carboxylic acids, including acetic acid and
propionic acid, at elevated temperature and pressure in the
presence of water and/or solvents using as catalyst
palladium/rhenium on a support, the palladium to rhenium weight
ratio of the catalyst being in the range from 0.01 to 5:1. The
process is operated at pressures in the range from 50 to 1000
atmospheres. The only processes exemplified are the hydrogenation
of C.sub.4 and higher dibasic acids at very high pressures
We have found that operation of a Group VIII noble metal catalyst
in the liquid phase suffers from the disadvantage that leaching of
both rhenium and Group VIII noble metal from the catalyst can
occur. Not only leaching of the catalytic metals but also
undesirable leaching of oxide-containing supports can occur. We
have now suprisingly found that operation in the vapour phase
provides high and comparatively long-lived catalytic activity and
selectivity at lower pressures than those previously employed.
Furthermore, operation in the vapour phase substantially overcomes
the leaching problem associated with liquid phase operation.
Accordingly, the present invention provides a process for the
production of either ethanol from acetic acid or propanol from
propionic acid which process comprises contacting either acetic
acid or propionic acid in the vapour phase with hydrogen at
elevated temperature and a pressure in the range from 1 to 150 bar
in the presence of a catalyst comprising as essential components
(i) a noble metal of Group VIII of the Periodic Table of the
Elements, and (ii) rhenium.
In addition to the alcohol, the process of the invention generally
produces the corresponding ester as a by-product, for example the
hydrogenation of acetic acid generally also produces ethyl acetate
and the hydrogenation of propionic acid generally also produces
propyl propionate. The proportion of the ester in the product may
be increased, if desired, by for example operating at low
conversions, for example at less than 50% conversion per pass, or
by introducing an acidic function into the catalyst to promote `in
situ` esterification. Alternatively, the proportion of alcohol may
be increased, for example by co-feeding water or by operating at
very high conversions per pass.
Both acetic and propionic acids are commercially available in large
tonnages and may be used in the process of the present invention in
their commercially available forms without further purification.
Alternatively, they may be further purified if desired.
Hydrogen, too, is commercially available on a large scale and may
be used with or without further purification.
The catalyst comprises a first component which is a noble metal of
Group VIII and a second component which is rhenium. For the
avoidance of doubt, the noble metals of Group VIII are the metals
osmium, palladium, platinum, rhodium, ruthenium and iridium. Of the
aforesaid metals of Group VIII, palladium and ruthenium are
preferred.
Preferably the catalyst further includes a support. Suitable
supports include high surface area graphitised carbons, graphites,
silicas, aluminas and silica/aluminas, of which high surface area
graphitised carbons and silicas are preferred. Preferred silica
supports are those having a high surface area, typically greater
than 50 m.sup.2 /g.
Particularly preferred supports are the high surface area
graphitised carbons described in GB-A-2136704 (BP Case No. 5536).
The carbon is preferably in particulate form e.g. as pellets. The
size of the carbon particles will depend on the pressure drop
acceptable in any given reactor (which gives a minimum pellet size)
and reactant diffusion constrant within the pellet (which gives a
maximum pellet size). The preferred minimum pellet size is 0.5 mm
and the preferred maximum is 10 mm, e.g. not more than 5 mm.
The carbons are preferably porous carbons. With the preferred
particle sizes the carbon will need to be porous to meet the
preferred surface area charateristics.
Carbons may be characterised by their BET, basal plane, and edge
surface areas. The BET surface area is the surface area determined
by nitrogen adsorption using the method of Brunauer Emmett and
Teller J. Am. Chem. Soc. 60,309 (1938). The basal plane surface
area is the surface area determined from the heat of adsorption on
the carbon of n-dotriacontane from n-heptane by the method
described in Proc. Roy. Soc. A314 pages 473-498, with particular
reference to page 489. The edge surface area is the surface area
determined from the heat of adsorption on the carbon of n-butanol
from n-heptane as disclosed in the Proc. Roy. Soc. article
mentioned above with particular reference to page 495.
The preferred carbons for use in the present invention have a BET
surface area of at least 100 m.sup.2 /g, more preferably at least
200 m.sup.2 /g, most preferable at least 300 m.sup.2 /g. The BET
surface area is preferably not greater than 1000 m.sup.2 /g, more
preferably not greater than 750 m.sup.2 /g.
The ratio of BET to basal plane surface area is preferably not
greater than 4:1, more preferably not greater than 2.5:1. It is
particularly preferred to use carbons with ratios of BET to basal
plane surface area of not greater than 1.5:1.
It is preferred to use carbons with ratios of basal plane surface
area to edge surface area of at least 10:1, preferably at least
100:1. It is not believed that there is an upper limit on the
ratio, although in practice it will not usually exceed 200:1.
The preferred carbon support may be prepared by heat treating a
carbon-containing starting material. The starting material may be
an oleophillic graphite e.g. prepared as disclosed in GB 1,168,785
or may be a carbon black.
However, oleophillic graphites contain carbon in the form of very
fine particles in flake form and are therefore not very suitable
materials for use as catalyst supports. We prefer to avoid their
use. Similar considerations apply to carbon blacks which also have
a very fine particle size.
The preferred materials are activated carbons derived from
vegetable materials e.g. coconut charcoal, or from peat or coal or
from carbonizable polymers. The materials subjected to the heat
treatment preferably have particle sizes not less than these
indicated above as being preferred for the carbon support.
The preferred starting materials have the following
characteristics: BET surface area of at least 100, more preferably
at least 500 m.sup.2 /g.
The preferred heat treatment procedure for preparing carbon
supports having the defined characteristics, comprise successively
(1) heating the carbon in an inert atmosphere at a temperature of
from 900.degree. C. to 3300.degree. C., (2) oxidizing the carbon at
a temperature between 300.degree. C. and 1200.degree. C., (3)
heating in an inert atmosphere at a temperature of between
900.degree. C. and 3000.degree. C.
The oxidation step is preferably carried out at temperatures
between 300.degree. and 600.degree. C. when oxygen (e.g. as air) is
used as the oxidising agent.
The duration of the heating in inert gas is not critical. The time
needed to heat the carbon to the required maximum temperature is
sufficient to produce the required changes in the carbon.
The oxidation step must clearly not be carried out under conditions
such that the carbon combusts completely. It is preferably carried
out using a gaseous oxidizing agent fed at a controlled rate to
avoid over oxidation. Examples of gaseous oxidising agents are
steam, carbon dioxide, and gases containing molecular oxygen e.g.
air. The oxidation is preferably carried out to give a carbon
weight loss of at least 10% wt based on weight of carbon subjected
to the oxidation step, more preferably at least 15% wt.
The weight loss is preferably not greater than 40% wt of the carbon
subjected to the oxidation step, more preferably not greater than
25% wt of the carbon.
The rate of supply of oxidizing agent is preferably such that the
desired weight loss takes place over at least 2 hours, more
preferably at least 4 hours.
Where an inert atmosphere is required it may be supplied by
nitrogen or an inert gas.
Suitably the catalyst comprises from 0.1 to 10% by weight Group
VIII noble metal preferably from 0.5 to 5% by weight Group VIII
noble metal and from 0.1 to 20% by weight rhenium, preferably from
1 to 10% by weight rhenium, the remainder of the catalyst
comprising the support.
The catalyst may be further modified by the incorporation of a
metal or metals of Group IA, Group IIA or Group IVA, preferably by
a metal of Group IA of the Periodic Table of the Elements. A
suitable metal is potassium. The amount of the modifying metal(s)
may suitably be in the range from 0.1 to 20% by weight based on the
total weight of the catalyst. The addition of a modifying metal to
the catalyst can have the advantageous effect that carbon-carbon
bond hydrogenolysis can be supressed to a greater or lesser extent
during the hydrogenation, thereby improving the selectivity of the
process to desired products.
The catalyst may be prepared by a variety of methods. One method of
preparing the catalyst comprises impregnating the support with an
aqueous solution of soluble compounds of rhenium and the Group VIII
noble metal which compounds are thermally decomposable/reducible to
the metal and/or metal oxide.
Impregnation may be by way of co-impregnation or sequential
impregnation, preferably by sequential impregnation. Sequential
impregnation is preferably effected in the order Group VIII noble
metal followed by rhenium.
A preferred method of producing a catalyst for use in the process
of the present invention comprises the steps of:
(A) impregnating a support with a solution of a soluble Group VIII
noble metal compound thermally decomposable/reducible to Group VIII
noble metal and subsequently removing the solvent therefrom,
and
(B) impregnating the Group VIII metal impregnated support with a
solution in a solvent in which the Group VIII metal is
substantially insoluble of a soluble rhenium compound thermally
decomposable/reducible to rhenium metal and/or an oxide and
thereafter removing the solvent therefrom.
Water may suitably be employed as the solvent in step (A) and a
lower alkanol, for example ethanol, may be used as the solvent in
step (B). The production of a catalyst in the aforesaid manner can
avoid the palladium impregnated on the support in step (A) being
leached to any appreciable extent in step (B) of the process.
Another preferred method of producing a catalyst for use in the
process of the present invention comprises the steps of:
(A') impregnating a support with a solution of a soluble Group VIII
noble metal compound thermally decomposable/reducible to the Group
VIII noble metal and subsequently removing the solvent
therefrom,
(B') heating the Group VIII noble metal on the support, and
(C') impregnating the Group VIII noble metal impregnated support
with a solution of a soluble rhenium compound thermally
decomposable/reducible to rhenium metal and/or oxide and thereafter
removing the solvent therefrom.
The Group VIII noble metal on the support may suitably be heated in
the presence of either an inert gas, for example nitrogen, a
reducing gas, for example hydrogen, or an oxygen-containing gas,
for example air. Heating in the presence of an inert gas may
suitably be accomplished at an elevated temperature in the range
from 150.degree. to 350.degree. C. Heating in the presence of a
reducing gas may suitably be accomplished at an elevated
temperature in the range from 100.degree. to 350.degree. C. Heating
in the presence of an oxygen-containing gas may suitably be
accomplished at an elevated temperature in the range from
100.degree. to 300.degree. C., provided that when a high surface
area graphitised carbon is used as support the upper temperature
limit is 200.degree. C.
In this embodiment of the invention it is not necessary that a
solvent in which the Group VIII metal is substantially insoluble be
used in step (C') of the process. Thus any suitable solvent may be
used in steps (A') and (C') of the process. Suitable solvents
include independently water and alkanols.
An advantage of the heating step (step (B')) is that the noble
metal of Group VIII is rendered less prone to leaching in step (C')
of the process.
Preferably, a further step is interposed either between step (A)
and step (B) or between step (A') and step (B') wherein the Group
VIII noble metal impregnated support is dried, suitably by heating
at a temperature in the range from 50.degree. to 150.degree. C. It
will be appreciated by those skilled in the art that this step may
be incorporated into step (B'), if desired.
Suitable Group VIII noble metals which are decomposable/reducible
to the metal include salts of the metals, for example carboxylates,
nitrates and compounds in which the Group VIII noble metal is
present in the anion moiety, for example ammonium
tetrachloropalladate and ammonium tetranitropalladate. Suitable
rhenium compounds which are decomposable/reducible to rhenium metal
and/or oxide include dirhenium decarcabonyl, ammonium perrhenate
and rhenium heptoxide.
The metal of Group IA, Group IIA or Group IVA of the Periodic Table
of the elements may be added to the catalyst composition at any
point during its preparation. Thus, the supported palladium/rhenium
catalyst may be impregnated with a solution of a soluble compound
of the metal. Alternatively, a soluble compound of the metal may be
added to the co-impregnation solution or either of the sequential
impregnation solutions.
A preferred catalyst comprises palladium and rhenium supported on a
high surface area graphitised carbon of the type described in the
aforesaid GB-A-2136704. Contrary to the teaching of the aforesaid
EP-A-0147219 (cf Comparison C) regarding unacceptable selectivity
losses and undesirable productivity losses in the hydrogenation of
maleic acid when the average palladium crystallite size is 100
Angstroms or less, we have found that in the hydrogenation of
acetic or propionic acids the catalyst selectivity and productivity
is substantially independent of average palladium crystallite size
in the range from 30 to 150 Angstroms. We may therefore use
catalysts in which the average palladium crystallite size is in the
range from 30 to 99.9 Angstroms.
Before use in the process of the invention the catalyst is
preferably activated by contact at elevated temperature with either
hydrogen or a hydrogen/inert gas, for example nitrogen, mixture for
a period of from 1 to 20 hours. The elevated temperature may
suitably be in the range from 200.degree. to 350.degree. C.
Alternatively, the catalyst may be activated by heating to the
reaction temperature in the presence of the reactants.
Whilst the precise nature of the catalyst on the support can not be
determined with any degree of confidence, it is believed that the
Group VIII noble metal component is in the form of the elemental
metal and the rhenium component is in the form of the elemental
metal and/or an oxide thereof.
The process of the invention may suitably be operated at an
elevated temperature in the range from 100.degree. to 350.degree.
C., preferably from 150.degree. to 300.degree. C. The pressure may
suitably be less than 50 bar.
The process may be operated batchwise or continuously, preferably
continuously. The catalyst may be employed in the form of a fixed
bed, a moving bed or a fluidised bed. The Gas Hourly Space Velocity
for continuous operation may suitably be in the range from 50 to
50,000 h.sup.-1, preferably from 2000 to 30,000 h.sup.-1.
The process of the invention will now be further illustrated by
reference to the following Examples.
CATALYST PREPARATION
Catalysts were prepared according to the procedures outlined below.
In the procedures, HSAG carbon denotes high surface area
graphitised carbon, prepared and characterised as follows:
The carbon used as support was prepared from a commercially
available activated carbon sold by Degussa under the designation BK
IV. The activated carbon was heat treated as follows. The carbon
was heated from room temperature in a stream of argon to
1700.degree. C. over a period of about one hour. When the
temperature reached 1700.degree. C. the carbon was allowed to cool
in the stream of argon to 25.degree. C. The carbon was then heated
in air in a muffle furnace at approximately 520.degree. C. for a
time known from experience to give a weight loss of 20% wt. The
carbon was then heated in argon to between 1800.degree. C. and
1850.degree. C. in argon. The carbon was allowed to cool to room
temperature in an argon atmosphere. The resulting
graphite-containing carbon was then ground to 16-30 mesh BSS.
The resulting carbon had the following properties:
______________________________________ BET surface area 710 m.sup.2
/g basal plane surface area 389 m.sup.2 /g edge surface area 2.3
m.sup.2 /g BET/basal surface area ratio 1.83 basal plane/edge
surface area ratio 169 ______________________________________
EXAMPLE 1
In the following procedures nominal loading is defined as weight of
metal (not salt) added to the support expressed as a percentage of
the weight of support.
A. An aqueous solution containing dissolved palladium nitrate and
rhenium heptoxide (Re.sub.2 O.sub.7) was added to HSAG carbon. The
water was removed on a rotary evaporator, and the resulting
impregnated carbon was then dried at 100.degree. C. in a vacuum
oven overnight. The amounts of the various components were chosen
to give four catalysts with nominal loadings as follows: A1-2.5%
Pd, 5% Re; A2-2.5% Pd, 2% Re; A3-2.5% Pd, 10% Re; A4-5% Pd, Re
excluded from the preparation.
B. The procedure used in the preparation of catalyst A was
followed, except that an appropriate amount of ammonium perrhenate
was used instead of Re.sub.2 O.sub.7, and the amounts of components
were chosen to give four catalysts with nominal loadings as
follows:
B1-5% Re, 2.5% Pd; B2-5% Re, 10% Pd; B3-5% Re, 0.5% Pd; B4-5% Re,
Pd excluded.
C. An aqueous solution of palladium nitrate was added to HSAG
carbon, the solvent was removed on a rotary evaporator, and the
resulting impregnated carbon catalyst dried overnight at
100.degree. C. in a vacuum oven. The catalyst was then cooled and
transferred to a glass tube, and was then heated in a stream of
hydrogen from ca 30.degree. to 280.degree. C. over a period of six
hours. After ten hours at 280.degree. C., the catalyst was cooled
under hydrogen, and then purged for several hours with
nitrogen.
The palladium on carbon was then mixed with an aqueous solution of
Re.sub.2 O.sub.7, the solvent again removed on a rotary evaporator,
and the catalyst dried overnight at 100.degree. C. in a vacuum
oven. The amounts of palladium nitrate and rhenium heptoxide were
chosen to give nominal loadings of 2.5% Pd and 5% Re in the final
catalyst.
D. The procedure used in the preparation of catalyst C was
repeated, except that prior to impregnation of rhenium, the
palladium impregnated carbon catalyst was treated in nitrogen at
300.degree. C. instead of hydrogen at 280.degree. C.
E. The procedure used in the preparation of catalyst C was
repeated, except that the hydrogen treatment step prior to
impregnation of rhenium was replaced by an air treatment step as
follows. The palladium impregnated carbon was heated from
20.degree. to 180.degree. C. in flowing air over six hours, and
held at 180.degree. C. for four hours, before cooling in air to
30.degree. C.
F. This catalyst was prepared according to procedure C except that
after drying, the palladium on carbon catalyst was not heated in
hydrogen, and the solvent used for the impregnation of rhenium was
ethanol instead of water.
G. Procedure C was used, except that immediately before the rhenium
impregnation stage, the reduced palladium on carbon catalyst was
treated in flowing nitrogen by heating from 30.degree. C. to ca
650.degree.-700.degree. C. over three hours, holding at
650.degree.-700.degree. C. for a further sixteen hours, and then
cooling to 30.degree. C. The effect of this additional step was to
increase the palladium crystallite size (as measured by XRD) from
30 Angstrom (catalyst from procedure C) to 150 Angstrom (catalyst
from this procedure).
H. Catalysts containing ruthenium, rhenium and potassium were
prepared as follows. HSAG carbon was mixed with a solution
containing ruthenium trichloride and ammonium perrhenate, the
solvent was removed on a rotary evaporator, and the resulting
catalysts dried ca 100.degree. C. overnight in a vacuum oven. The
catalyst was then heated in flowing hydrogen from ca 30.degree. to
300.degree. C. over two hours, held at 300.degree. C. for one hour,
then cooled under hydrogen and purged with nitrogen. The reduced
catalysts were then impregnated with potassium from an aqueous
solution of potassium acetate. The amounts of the various
ingredients were adjusted to give four catalysts with nominal
loadings as follows:
H1-5% Re, 5% Ru, (K excluded); H2-5% Re, 5% Ru, 10% K; H3-5% Ru, 5%
K (Re excluded); H4-5% Ru (Re and K excluded).
I. A catalyst containing ruthenium and rhenium was prepared
according to procedure C, except that ruthenium nitrosyl nitrate
replaced palladium nitrate, the ruthenium on carbon catalyst was
dried at 120.degree. C. not 100.degree. C., and was then heated in
hydrogen to 300.degree. C. at 4.degree. C./minute, and held at
300.degree. C. for one hour. The amounts of the ingredients were
chosen to give nominal loadings of 1% ruthenium and 10%
rhenium.
J. A ruthenium/rhenium catalyst was prepared as in procedure I,
except that rhenium was impregnated first.
K. Procedure A was used except that HSAG carbon was replaced by
Davison 57 silica, ammonium tetrachloropalladate was used instead
of palladium nitrate, and only one catalyst containing nominally
2.5% Pd and 5% Re was prepared.
L. Procedure C was used for the preparation of a catalyst
containing platinum and rhenium. Tetrammine platinuous hydroxide
replaced palladium nitrate, and the nominal loadings were 1% Pt and
5% Re.
CATALYST TESTING
For experiments at pressures in the range 1-11 barg, 2.5 mls of
catalyst was loaded into a corrosion resistant stainless steel tube
of internal diameter 6-7 mm, and the reactor tube assembly placed
in a tubular furnace. The catalyst was then activated by heating at
atmospheric pressure in a stream of hydrogen to either 280.degree.
or 300.degree. C. over a two hour period, and then holding at the
final temperature for one hour. After activation, the catalyst was
cooled in hydrogen to the desired reaction temperature. A mixture
of carboxylic acid vapour and hydrogen was then passed over the
catalyst, and pressure was adjusted to the required value by means
of a back-pressure regulator. The vapour/hydrogen mixture was
formed in a vapourising zone, to which acetic acid liquid and
hydrogen gas were separately metered. The product vapours andgases
leaving the reactor were sampled on-line and analysed by gas-liquid
chromatography (glc).
For experiments conducted at 11-50 barg, a similar procedure and
apparatus was used, except that the tube had internal diameter 10
mm, up to 10 mls of catalyst was employed, and products were passed
to a condenser, and gas and liquid products were analysed
separately, again by glc.
In both procedures, temperature was measured by means of a
thermocouple inserted into the catalyst bed.
The product mixtures typically contained the appropriate alcohol
and ester (the latter formed by esterification of alcohol with
unreacted acid), together with traces of the appropriate dialkyl
ether, and aldehyde, and by-product methane, ethane and (with
propionic acid only) propane. In general, with carbon and silica
supported catalysts, the main product is alcohol, especially at
high conversions.
For the purposes of the Examples, conversions and selectivities
have been calculated as respectively, the proportion of carboxylic
acid hydrogenated, and the proportion of the hydrogenated
carboxylic acid which is not converted into alkane by-product.
Thus, selectivity denotes the ability of the catalyst to carry out
hydrogenation without alkanation. In all examples (unless stated
otherwise) only trace amounts (.ltoreq.2%) of dialkyl ether and
aldehyde are formed.
DEFINITIONS
WHSV=Weight Hourly Space Velocity=kg liquid feed per kg catalyst
per hour.
LHSV=Liquid Hourly Space Velocity=liters liquid feed per liter of
catalyst per hour.
Productivity=kg acid converted per kg catalyst per hour.
EXAMPLES 2-7
Acetic acid was hydrogenated over the catalysts prepared in
procedure A Example 1, and procedure C Example 1. The WHSV was ca
1.1 (LHSV=0.35), the ratio hydrogen to acetic acid was ca 11:1
molar, and the pressure was 10.3 barg. In each case the catalyst
was activated at 300.degree. C., except for the catalyst of Example
7 (C), which was activated at 280.degree. C. The results are
collected in Table 1. Steady catalyst activity was observed in all
cases. No deactivation was observed over run periods of up to 24
hours.
TABLE 1 ______________________________________ Conversion
Selectivity Example Catalyst T/.degree.C. (%) (%)
______________________________________ 2 A1 222 27.2 91 3 A1 202
15.0 90 4 A2 202 6.3 93.6 5 A3 201 38.2 95.9 6 A4 200 0.6 30.4 7 C
217 52.1 93 ______________________________________
The results show the benefit of sequential impregnation of Pd and
Re (Example 7), and the poor performance of catalyst A4 (Example
6), which contains only palladium, and is not a catalyst according
to the invention.
EXAMPLES 8-13
The same procedure as in Examples 2-7 was followed, but using the
catalysts prepared according to procedure B Example 1. All
catalysts were activated at 300.degree. C. Results are presented in
Table 2.
TABLE 2 ______________________________________ Conversion
Selectivity Example Catalyst T/.degree.C. (%) (%)
______________________________________ 8 B1 180 15.4 97.0 9 B1 210
37.5 95.1 10 B1 239 69.0 89.0 11 B2 210 45.0 95.0 12 B3 210 18.5
96.9 13 B4 210 13.7 97.6 ______________________________________
The Catalyst of Example 13 is not according to the present
invention, and is included for the purposes of comparison.
EXAMPLES 14-17
The catalyst prepared by procedures C, D, E and F of Example 1 were
compared in the hydrogenation of acetic acid. The procedure of
Examples 2-7 was followed, except that the WHSV was ca 4
(LHSV=1.34), and the ratio hydrogen to acetic acid was 9:1 molar.
The catalysts were activated at 280.degree. C. before use, and the
reaction temperature was 228.degree.-230.degree. C. Results are
collected in Table 3.
TABLE 3 ______________________________________ Productivity
Selectivity Example Catalyst (kg/kg cat/h) (.degree.C.)
______________________________________ 14 C 1.2 92.2 15 D 1.3 92.1
16 E 1.1 87.0 17 F 0.95 94.5
______________________________________
The results show that within experimental error, catalysts of
similar high activity may be generated using a range of sequential
impregnation techniques.
EXAMPLES 18
The procedure of Examples 14-17 was repeated using the catalyst
prepared according to procedure G Example 1. The productivity was
found to be 1.0 kg/kg cat/h, with 92.7% selectivity. Within
experimental error, these results are similar to those obtained in
Example 14, even though the catalyst of this Example has Pd
crystallites (as determined by XRD) of average size 150 Angstrom,
whereas that of Example 14 has an average Pd crystallite size of
only 30 Angstrom. The results show that no significant losses of
activity and selectivity result when catalysts containing small Pd
crystallites of <100 Angstrom are employed in contrast to the
teaching of EP-A-147219 (Comparison C).
EXAMPLE 19
The catalyst prepared by procedure C was tested in acetic acid
hydrogenation at 50 barg and 227.degree. C. The WHSV was 15, and
the ratio hydrogen:acetic acid was 9:1 molar. The catalyst was
activated at 280.degree. C.
The acetic acid conversion was 40%, with 96% selectivity. This
corresponds to a productivity of 6 kg/kg cat/h acetic acid
converted. Under similar conditions but with WHSV=3.6, conversion
was 74% with 96% selectivity.
EXAMPLES 20-24
The catalysts prepared by procedure H were tested in the
hydrogenation of acetic acid. The catalysts were activated at
300.degree. C. The WHSV was ca 1.1 (LHSV=0.35), and the ratio
hydrogen to acetic acid was 11:1 molar. Results are collected in
Table 4.
TABLE 4 ______________________________________ Conversion
Selectivity Example Catalyst P/barg T/.degree.C. (%) (%)
______________________________________ 20 H1 5 200 46 38 21 H2 5
202 43 53 22 H2 10 194 54 58.5 23 H3 10 203 35.2 8.7 24 H4 5 201
22.3 5.9 ______________________________________
The results show the beneficial effect of potassium in improving
selectivity, and that catalysts H3 and H4 which are not according
to the present invention, show very poor performance.
EXAMPLES 25-28
Catalysts prepared by procedures I and J of Example 1 were examined
in the hydrogenation of propionic acid. The procedure of Examples
2-7 was repeated, except that only 2 mls of catalyst was employed,
LHSV=1, the ratio of propionic acid to hydrogen was 1:10 molar, the
pressure was 9 barg, and the catalyst were activated at 280.degree.
C. Results are collected in Table 5. In each case, the
concentration of aldehyde in the product was greater than the trace
amounts encountered in other Examples. Independent selectivities to
aldehyde are therefore reported.
TABLE 5 ______________________________________ Ex- Cata- Conversion
Selectivity Selectivity ample lyst T/.degree.C. (%) (%) (%
aldehyde) ______________________________________ 25 I 202 22.5 97 4
26 I 223 32.0 94 3 27 J 201 12.5 97 5 28 J 222 23.0 96 5
______________________________________
The results show that sequential impregnation of Ru then Re yields
better catalysts than sequential impregnation of Re then Ru.
EXAMPLES 29 AND 30
The catalysts prepared by procedure K Example 1 were tested in the
hydrogenation of acetic acid. The procedure of Examples 2-7 was
adopted, except that the catalyst of Example 30 was activated at
450.degree. C., and that of 29.degree. at 300.degree. C. Results
are collected in Table 6.
TABLE 6 ______________________________________ Conversion
Selectivity Example Catalyst T/.degree.C. (%) (%)
______________________________________ 29 K 209 12.2 91.7 30 K 210
10.5 95.3 ______________________________________
EXAMPLE 31
The catalyst prepared by procedure L was employed for the
hydrogenation of acetic acid, according to the procedure of
Examples 14-17. The conversion was 11.0% (productivity 0.5 kg/kg
cat/h converted) with 93.8% selectivity.
EXAMPLE 32
The catalyst prepared according to procedure B1 was used for the
liquid phase hydrogenation of acetic acid. 1.01 g of the powdered
catalyst was charged to a 100 ml stainless steel autoclave, along
with 50.2 g of acetic acid. The autoclave was flushed and then
pressurised with hydrogen to 100 barg, and heated with stirring to
200.degree. C., at which temperature it was held for 6.0 hours.
After cooling, the liquid phase product was removed and filtered,
and analysed both for organic products and rhenium and palladium
metals. The final pressure after cooling was 50 barg.
The product was found to contain 27.9% wt ethyl acetate and 2% wt
ethanol (corresponding to a productivity of 1.5 kg/kg cat/h
converted by hydrogenation). In addition, 16% of the rhenium and
0.06% of the palladium originally on the catalyst was found to have
leached into solution.
This example demonstrates that considerable leaching of rhenium can
occur in the liquid phase hydrogenation of acetic acid. This is in
contrast to reactions carried out in the gas phase, where no
detectable loss of rhenium occurs.
This is not an example according to the present invention because
it was carried out in the liquid phase. It is included only for the
purpose of comparison.
* * * * *